The present invention relates to nacreous pigments having improved light fastness which are based on mica platelets coated with titanium dioxide and additionally, if appropriate, other metal oxides.
In the preparation of pigments, it is a fundamental desire to improve the light fastness. In particular, in order to improve the light fastness of mica flakes coated with titanium dioxide, numerous processes have already been proposed. Thus, German Pat. No. 1,467,468 (U.S. Pat. No. 3,087,828) proposes to apply a top layer of aluminum oxide, zirconium oxide, zinc oxide, tin oxide, antimony oxide, iron oxide, nickel oxide, cobalt oxide, copper oxide or chromium oxide for this purpose. German Offenlegungsschrift No. 2,106,613 proposes a subsequent treatment with silicate, and in German Offenlegungsschrift No. 2,215,191 and German Offenlegungsschrift No. 2,852,585, coatings of methacrylatochromium(III) chloride and of chromium hydroxide are applied respectively.
Nevertheless, there still exists a need for pigments which, on the one hand, have very good light fastness but, on the other hand, can also be prepared in an economical manner and provide interesting color effects.